It's worth bearing in mind though that the Buddha did not discourage people from making offering to wanderers of other sects, even though their ascetics and practitioners were to certain extents ignorant.
Kamma is intention and it's not transcendent, so it's to be expected that there will be some degree of imperfection associated with any volitional act.
"Do not force others, including children, by any means whatsoever, to adopt your views, whether by authority, threat, money, propaganda, or even education." - Ven. Thich Nhat Hanh
"The uprooting of identity is seen by the noble ones as pleasurable; but this contradicts what the whole world sees." (Snp 3.12)
"To argue with a person who has renounced the use of reason is like administering medicine to the dead" - Thomas Paine